Common smartphones, phablets, or comparable mobile electronic devices contain a front-facing camera placed on the front side of the mobile electronic devices. The front side of the mobile electronic devices also contains a display screen, using a display technology such as liquid-crystal display (LCD) or active-matrix organic light-emitting diode (AMOLED).
For example, the display may use an LC panel. The LC panel may include a thin film transistor (TFT) substrate, a color filter substrate, and LC molecules injected between the TFT substrate and the color filter substrate. The TFT substrate may include gate lines and data lines implemented as matrices. Thin film transistors (TFT) may be formed at crossing points of the gate lines and the data lines. A signal voltage is applied to a common electrode disposed between a pixel electrode and the color filter substrate. Liquid crystal molecules are aligned between the pixel electrode and the common electrode according to the signal voltage, thereby controlling light transmittance. The color filter substrate may include a color filter and a common electrode, the color filter having red, green, and blue filters repeatedly formed in a state where black matrices are disposed therebetween. The common electrode may be formed of a transparent conductive material, such as indium tin oxide (ITO) or indium zinc oxide (IZO).
A pair of polarizers may be arranged on the upper and lower surfaces of the LC panel. The polarizers may be arranged to cross each other. The polarizer disposed under the LC panel serves to polarize light incident onto the LC panel, and the polarizer formed on the LC panel serves as an analyzer. A backlight unit may be disposed beneath the LC panel. The backlight unit may include a diffusion sheet, a reflection sheet, and a prism sheet.
In another example, the display panel may be implemented as an AMOLED display consisting of several layers, e.g., cathode layer, organic active layers, thin-film transistor (TFT) array, and substrate. An active matrix of OLED pixels generates light (luminescence) upon electrical activation. The active matrix of OLED pixels may be deposited or integrated onto the thin-film transistor (TFT) array, which functions as a series of switches to control the current flowing to each individual pixel. Known TFT backplane technologies, such as polycrystalline silicon (poly-Si) and amorphous silicon (a-Si), may be used. The display panel may be a flexible display, which enables the display panel to be bent, rolled, or curved at the edges. For example, a flexible OLED-based display may comprise a flexible substrate on which the electroluminescent organic semiconductor is deposited. Optionally, the display panel may have an in-cell touch panel that integrates a capacitive sensor array.
The display screen may be rectangular with an aspect ratio of, for instance, 16:9, 2:1, 19.5:9, or 21:9. Furthermore, display panels with a round shape are known from the prior art. More information about the assembly and structure of round displays (e.g., for smartwatches) can be found, inter alia, in patent application US2017/0168463 A1, titled “Display panel with minimum borders” and patent application US2016/0313593 A1, titled “Divided backlight configuration of a display.”
A smartphone with a rectangular display screen may be oriented horizontally or vertically by the user, which may result in operating modes known as “landscape mode” and “portrait mode,” respectively. The page orientation can also be described with the terms “landscape orientation” and “portrait orientation.”
A user may hold the smartphone horizontally (landscape mode) and may watch a video or movie displayed in full screen mode on the display screen. A feature film or a wide-screen movie may have an aspect ratio of, e.g., 2.35:1, 2.39:1, 2.40:1, or 2.66:1. If the wide-screen movie has an aspect ratio that is wider, i.e., greater, than the aspect ratio of the display screen, the wide-screen movie frames may be displayed on the display screen in a mode known as “letterbox”: horizontal bars, typically black bars, are inserted above and below the wide-screen movie.
The display screen of a smartphone typically does not occupy the full front side of the smartphone because a wide border is required at the top and/or at the bottom of the front side to accommodate the lens of a front-facing camera and also to accommodate other optical or acoustic sensors and emitters. As a result, the size of the display screen is reduced.
The front-facing camera of a smartphone may be used for video telephony or to take a self-portrait photograph, commonly known as a “selfie.” In recent years, the resolution of the front-facing camera has increased, and it is likely that the resolution will continue to increase in the future (e.g., from 8 megapixels to 13 megapixels) to enable the user to take “selfies” of the highest quality and to record high-quality 4K videos. Therefore, high-quality camera lenses for the front-facing camera and an undisturbed light path are essential.
Patent applications US2017/0123454 A1, US2017/0123453 A1, and US2017/0123452 A1, titled “Camera integrated into a display,” patent application US2017/0123575 A1, titled “Optical sensors disposed beneath the display of an electronic device,” patent application US2017/0124933 A1, titled “Mobile device with display overlaid with at least a light sensor,” patent applications US2017/0126979 A1 and US2017/0126937 A1, titled “Apparatus and method to maximize the display area of a mobile device,” and patent application US2015/0271392 A1, titled “System and method for coordinating image capture in a camera hidden behind a display device,” suggest disposing the front-facing camera beneath the display screen of the smartphone. However, depending on the display technology of the screen (e.g., LCD, OLED, Micro-LED, etc.), small opaque or semi-transparent structures that may be necessary for the operation of the display screen may blur or cloud the resulting picture of the front-facing camera, because the light path must pass through the display screen. Furthermore, LCD panels often also require removing a diffuser layer to adapt them for use as transparent displays, and the polarizing filters of the LCD panels inherently limit the transmission efficiency of unpolarized light. This may reduce the light sensitivity of a front-facing camera located beneath the display screen, especially in low-light conditions.